Cyclic poly(lactide)s via the ROPPOC method catalyzed by alkyl‐ or aryltin chlorides

Abstract

A comparison of tributyltin chloride, dibutyltin dichloride, and butyltin trichloride as catalysts of ring-opening polymerizations (ROPs) of l-lactides at 160 C in bulk reveals increasing reactivity in the above order, but only the least reactive catalysts, Bu 3 SnCl, yield a uniform reaction product, namely cyclic poly(L-lactide)s with weight average molecular weights (M w´s ) in the range of 40,000-80,000. A comparison of dimethyltin , dibutyltin , and diphenyltin dichlorides resulted in the following order of reactivity: Me 2 SnCl 2 < Bu 2 SnCl 2 < <Ph 2 SnCl 2 . In this series also, the most reactive catalyst yields cyclic polylactides, but the extent of cyclization varies with the molecular weight. The formation of cyclic polylactides is explained by ROP combined with simultaneous polycondensation involving end-to-end cyclization (ROPPOC method). ROP of meso-lactide at 80 or 60 C yields even-numbered linear chains as main products, a result supporting the ROPPOC mechanism.

Spirocyclic bisphenoxides of Ge, Zr, and Sn as catalysts for ring‐expansion polymerizations of l‐ and meso‐lactide

“…As exemplarily demonstrated in Figures (A) and (A) , the MALDI‐TOF mass spectra of the poly( l ‐lactide)s recovered from the experiments with GeNaph 2 or ZrNaph 2 at Lac/Cat ratios of 100/1 almost exclusively displayed mass peaks of cyclic poly( l ‐lactide)s with equal quantities of even‐ and odd‐numbered species. Analogous results were obtained with cyclic dibutyl tin catalysts as reported previously . They indicated that the REPs proceeding according to Scheme were followed by an intracircular “backbiting” equilibration (Scheme ), which was complete after 22 h (and most likely even before).…”

“…The data of Curve (C) are in good agreement with the best data of samples prepared via REP with other catalysts (e.g., ref. [] and unpublished data). Hence, it may be assumed that the extent of cyclization amounts to approximately 95%, in good agreement with mass spectrum of the low molar mass fraction [Fig.…”

“…Quite recently, the authors of this work have reported that the cyclic dibutyltin derivatives outlined in Scheme catalyze ring‐expansion polymerizations (REPs) at temperatures >100 °C . Since all active species exclusively involve covalent bonds and no ions, these REPs proceed without racemization even at 180 °C and weight‐average molecular weights in the range of 100,000–150,000 g mol −1 were obtained in numerous experiments.…”

Synthesis of cyclic polymers and flaws of the Jacobson–Stockmayer theory

“…Finally, it should be mentioned that after optimization of the reaction conditions cyclic polylactides were also obtained, when commercial tributyltin chloride or diphenyltin dichloride were used as catalysts due to the intermediate formation of acid chloride end groups. 28 Examples of MALDI mass spectra and MHS measurements were reproduced as Fig. S4 and S5 in the ESI.…”

High Tm poly(L-lactide)s via REP or ROPPOC of l-lactide

“…More recently, optically pure cyclic poly(L-lactide)s with M w values up to 300 000 g mol −1 were prepared either by ringexpansion polymerization (REP) with cyclic tin catalysts [15][16][17] or by the so-called ROPPOC approach, [18][19][20] which means simultaneous ring-opening polymerization and polycondensation. This mechanism initially generates linear chains having highly reactive end groups, so that low and high molecular weight cyclics are formed by back-biting and by end-to-end cyclization (Scheme 3).…”